The preferred embodiment of the present invention an index pulse to provide an absolute indication of the position of the code wheel. The described encoder provides a push-pull system using two tracks on an opaque code wheel to produce an index pulse. Applicant is not aware of any prior push-pull systems using opaque code wheels. By periodically providing structural sections so as to maximize the separation between the two signals of the push-pull system at positions other than those near the index position, an opaque code wheel which has a low possibility of a false comparison is provided. This provides an index pulse which is relatively immune to noise induced error.